Vacuum contact printing for the graphic arts has been known for a number of years. In this art, light-sensitive materials are placed in contact with a negative, such as a photographic negative, and exposed to light to provide a positive exposure on the light-sensitive material. One of the important aspects of this art is to be sure that the negative and the light-sensitive material are in intimate contact over their surfaces in order to assure a true image when the positive is exposed.
This is done by placing both the light-sensitive material and the negative in a chamber between a flexible blanket and a glass plate. The air between the blanket and glass plate is evacuated, so that atmospheric pressure on the other side of the blanket forces it against the plate, pressing the light-sensitive material and negative into intimate contact against the glass plate, through which light can be used to expose the light-sensitive material.
However, it has been found that at times air becomes trapped in the center of the space between the blanket and glass plate and cannot be evacuated, forming a bubble which causes distortions in the positive image being made on the light-sensitive material. Numerous proposals for overcoming this problem have been proposed, with varying degrees of success. Exemplary of vacuum printers, some of which attempt to overcome this problem are the disclosures of the following patents:
______________________________________ Patentee U.S. Pat. No. ______________________________________ Sigler et al. 2,956,769 Orr et al. 3,625,611 Harrell et al. 3,635,559 Wolf et al. 3,740,140 Topfer 3,995,955 Jacobs 4,089,603 Trankle 4,211,808 Takeuchi 4,360,266 Maher et al. 4,484,813 Richards, Sr. 4,504,142 Maher et al. 4,551,016 ______________________________________
Another device is shown in German Offenlegungsschrift - No. 2,230,111.
The foregoing devices all have various drawbacks, primarily including ineffectiveness and/or extra expense to implement.
The present invention fulfills the need in the art for an inexpensive and effective vacuum frame printer which eliminates the formation of such air bubbles.